Presentation on theme: "SITE REMEDIATION Pedro A. García Encina"— Presentation transcript:
1SITE REMEDIATION Pedro A. García Encina Department of Chemical EngineeringUniversity of Valladolid
2CONTAMINATED SITESIn the past much wastes were dumped indiscriminately or disposed of in inadequate facilities. These problems went ignored as did spills of product or leaks from tanks.Theses practices contaminated sites with hazardous substances that pose a threat to human populations.
3HAZARDOUS WASTE - Characteristics Corrosivity - waste that is highly acidic or alkaline, with pH <2 or pH >12.5.Ignitability - waste that is easily ignited.Reactivity - waste that is capable of sudden, harmful reaction or explosion.Toxicity - waste capable of releasing specified, toxic substances to water in significant concentrations.
4HAZARDOUS WASTE - Major Categories Inorganic Aqueous Waste - liquid waste composed of acids, alkalis or heavy metals in water.Organic Aqueous Waste - mixtures of hazardous organic substances (pesticides, petrochemicals) and water.Oils - liquid waste composed primarily of petroleum derived oils (lubrication oils, cutting fluids).Inorganic Sludges/Solids - sludges, dusts, solids, non-liquid wastes containing hazardous inorganic substances (metal fabricating wastes).Organic Sludges/Solids - tars, sludges, solids and other non-liquid wastes containing organic hazardous substances (contaminated soils).
5Toxicity Characteristics of Hazardous Wastes Acute Toxicity - results in harmful effects shortly after a single exposure, such as cyanide poisoning.Chronic Toxicity - may take up to many years to result in toxic effects, such as cancer or long-term illness.
10SITE REMEDIATION METHODOLOGY · SITE CHARACTERIZATION · REMEDIAL ALTERNATIVES ANALYSIS· DESIGN, CONSTRUCT AND OPERATE
11SITE CHARACTERIZATION - Definition Site Characterization is defined as the qualitative and quantitative description of the conditions on and beneath the site which are pertinent to hazardous waste management.
12SITE CHARACTERIZATION - Goals The goals of site characterization are to:1. Determine the extent and magnitude of contamination2. Identify contaminant transport pathways and receptors3. Determine risk of exposure
16METHODS OF SITE CHARACTERIZATION Remote MethodsSeismic SurveySoil ResistivityGround Penetrating RadarMagnetometer SurveyDirect MethodsAuger DrillingRotary DrillingSoil Excavation
17REMOTE SUBSURFACE CHARACTERIZATION Seismic SurveyShock wave propagates faster through rock than soil, depth to rock and rock type can be determined.Geologic WaveMaterial Velocity (m/s)Dry sandWet sandClayWaterSandstoneLimestoneGraniteSourceGeophonesSeismicwaveSoilRock
18REMOTE SUBSURFACE CHARACTERIZATION Soil ResistivitySoil/rock type can be determined by soil resistivity.R=soil resistivity(ohm-m)s=electrode spacing (m)V=measured voltage (volts)I=applied current (amperes)Current MeterBatteryResistivitySoil Type Range (ohm-m)Clays 1-150Alluvium and sand 100-1,500Fractured bedrock Low 1,000sMassive bedrock High 1,000sVoltage MetersCurrent flow lines
19DIRECT SUBSURFACE CHARACTERIZATION Auger DrillingUseful in unconsolidated geologic materials.Sample collection easy, intact samples can be collected with hollow-stem auger.Cannot be used where significant consolidated rock is present.Does not alter subsurface geo-chemistry.Rod inside hollow stem for removing plugFlightRemovablePlugDrill Bit
20DIRECT SUBSURFACE CHARACTERIZATION Rotary DrillingUseful in consolidated geologic materials, can drill through rock.Subsurface samples contaminated with drilling mud.Air-rotary may blow volatile contaminants into surrounding subsurface structures (basements).Mud-rotary alters subsurface chemistry.mud pumpmud pit
21DIRECT SUBSURFACE CHARACTERIZATION Drilling through confining layers may allow the spreadof contamination from one hydrologic unit to another.monitoring wellleakingtanksoilcontaminated ground waterconfining layer (clay)uncontaminated water
22DIRECT SUBSURFACE CHARACTERIZATION Soil ExcavationAdvantagesDisadvantagesNo specialized equipment, typically uses backhoe.Subsurface samples can be collected directly.Inexpensive.Good source removal mechanism.Useful only in unconsolidated geologic materials to a maximum depth of 10 meters.Large surface disturbance.Excavation not useful for long term groundwater monitoring.
23SOIL CHARACTERIZATION Soil Contaminant SamplingPerformed during drilling or excavation.Collection of samples from several depths within the soil profile.Where volatile compounds are present, sampling should be done in air-tight glass containers. No headspace should be left in the containers.Samples should be chilled for transportation to the laboratory.
24GROUNDWATER CHARACTERIZATION Extent of Contamination:Successive wells should be drilled until the extent of the groundwater contaminant plume is defined.
25AIRBORNE CONTAMINATION Source: Waste pileRelease Mechanism: VolatilizationTransport Medium: AirExposure Mechanism: Inhalation or skin contactExposure Point: May be distant from source, depends on concentration and wind speed
26AIRBORNE CONTAMINATION Measurement TechniquesLaboratory Analysis: Samples can be collected in the field in an air-tight bag (Tedlar™ ) and sampled in the laboratory.Field Analysis: Samples can be analyzed in the field via handheld instrumentation such as a photo-ionization detector for volatile organic compounds or a draw-tube collection device (such as a Drager™ tube).
27AIRBORNE CONTAMINATION Reducing Airborne HazardsAirborne Hazards Reduction can be accomplished through:Source removalCovering the source (prevents volatilization)Dilution with clean air (if indoors)
28ASSESSING EXPOSURE RISK Definition: Assessment of exposure risk seeks to determine the probability that contamination will migrate to a receptor (human or animal) and be ingested (eaten, inhaled, or absorbed by the skin).
30EXPOSURE PATHWAYS2Contaminated groundwater: exposure from drinking or from breathing contaminated vapors liberated during bathing341
31EXPOSURE PATHWAYS234Inhalation of airborne contaminants: volatilized from the source and carried by wind.1
32EXPOSURE PATHWAYS234Direct contact with contaminated soil: exposure from skin contact with contaminants in soil.1
33EXPOSURE PATHWAYS234Indirect contact: exposure to contaminant from crops or animals which have accumulated contamination from soil or groundwater1
34SITE REMEDIATION METHODOLOGY · SITE CHARACTERIZATION · REMEDIAL ALTERNATIVES ANALYSIS· DESIGN, CONSTRUCT AND OPERATE
35DEVELOPMENT OF ALTERNATIVES Identify general response to actions for each objectiveCharacterise media to be remediatedIdentify potential technologiesScreen the potential technologiesAssemble the screened technologies into alternatives
36ALTERNATIVE SELECTION 1. Long term effectiveness2. Long term reliability3. Implementability4. Short term effectiveness5. Cost
37ALTERNATIVE SELECTION 1. Long term effectiveness2. Long term reliability3. Implementability4. Short term effectiveness5. CostQualitative assessment of how well an alternative meets the remedial action objective over the long termTo calculate by means of a complete analysis the residual risk (Risk represented by untreated contaminants or residuals remaining at the site)
38ALTERNATIVE SELECTION 1. Long term effectiveness2. Long term reliability3. Implementability4. Short term effectiveness5. CostIs only a issue with the alternatives that leave untreated contaminants or treatment residuals at site at the conclusion of the implementation periodOne tradeoff that require careful consideration at most sites is whether to treat or to contain
39ALTERNATIVE SELECTION 1. Long term effectiveness2. Long term reliability3. Implementability Function of4. Short term effectiveness5. CostHistory of the demonstrated performance of a technologyAbility to construct and operate it given the existing conditions at the particular siteAbility to obtain the necessary permits from regulatory agencies
40ALTERNATIVE SELECTION 1. Long term effectiveness2. Long term reliability3. Implementability4. Short term effectiveness5. CostDeals primarily with the effects on human health an the environment of the remediation itself during its implementation phaseHealth and environmental riskWorker safetyImplementation time
41ALTERNATIVE SELECTION 1. Long term effectiveness2. Long term reliability3. Implementability4. Short term effectiveness5. CostThe weight given to the cost when evaluating alternatives depend upon the particular guidance of the agencyCapital costs (the cost to construct the remedy)Operating and maintenance cost (O & M) (post-construction expenditures)
42TREATMENT ALTERNATIVES On site· In situ· Ex situ (Excavation)Off site (Excavation & Transportation)
43HAZARDOUS WASTE TREATMENT METHODS Physical/Chemical Methods: Mass transfer and chemical transformation processes resulting in the removal or remediation of contamination by abiotic, not combustion means.Biological Methods: Transformation or binding of contaminants by microorganisms, principally bacteria.Waste Stabilization: Containment of wastes such that they pose no further threat to receptors.Combustion Methods: Transformation of organic wastes by burning.
44SOIL VAPOR EXTRACTIONDescription - soil vapor extraction (SVE) uses a vacuum applied to soil to remove volatile organic compounds (VOCs) from the unsaturated zone.Uses - effective for contaminants with high vapor pressure, such as gasoline compounds, chlorinated solvents.Advantages - low cost, simple design and operation, efficient removal of VOCs from unsaturated zone.Disadvantages - not effective for non-volatile compounds, not effective in low permeability soils or where groundwater is close to the surface, may need to treat off-gas in another process, does not address groundwater contamination.
45SOIL VAPOR EXTRACTION Vapor Extraction Pump contaminated soil air movement throughcontaminated soilWaterTableContaminated Groundwater
46AIR STRIPPINGDescription - enhances volatilization of dissolved contaminants from water. Can be used for treatment of either process wastewater or groundwater pumped to the surface.Uses - remove volatile organic compounds (VOCs) from water.Advantages - simple operation, efficient removal of low concentrations of VOCs.Disadvantages - high capital cost, design intensive, may need to treat off-gas in another process.
47Packed Column Air Stripper Water Inlet (contaminated)AirOutlet (contaminated)Types of Packing MaterialsIntalox saddleRaschig ringPall ringBerl saddleTri-packPacking MaterialWater Outlet (clean)Air Inlet (clean)
48Packed Column Air Stripper Typical Air-Stripping Column Specifications:Diameter: metersHeight: metersAir/Water ratio: 5-200Pressure drop: N/m2Stripping ColumnOff-gas Treatment System
49CARBON ADSORPTIONDescription - carbon adsorption uses granular activated carbon (GAC) to remove organic contaminants from a water or vapor stream. Contaminated air/water is pumped through the GAC unit and contaminants adsorb onto carbon particles by electrostatic forces.Uses - effective for a wide range of organic contaminants. Is commonly used both for process waste treatment and for hazardous waste remediation.Advantages - easy to install, can completely remove many organics, can treat either water or vapor stream.Disadvantages - high operating expense, carbon must be changed periodically, contaminants are not mineralized.
50SOIL WASHING OR FLUSHING Description - Excavated soil is flushed with water or other solvent to leach out contamination. Based on the principles of solid-liquid extractionUses - remove organic wastes and certain (soluble) inorganic wastesAdvantages - simple operation, efficient removal of organic contaminants (VOC, semi VOC and halogenated organics) . For metal, it has been successful at extracting organically bound metals (tetraethyl lead)Disadvantages - Longer washing times and soil-handling problems with lower-permeability clays and clay-like soils
52CHEMICAL OXIDATIONDescription - organic chemicals in extracted groundwater or industrial process wastewater are transformed into less harmful compounds through oxidation by ozone (O3), hydrogen peroxide (H2O2), chlorine (Cl2) or ultraviolet radiation (UV). UV is often used in combination with ozone or hydrogen peroxide.Uses - effective for a wide range of organic contaminants such as VOCs, mercaptians, and phenols. Can also be used for some inorganics, such as cyanide. Process is non-specific, oxidant will react with any reducing agent present in the waste, such as naturally occurring organic matter.Advantages - effective, reliable treatment for waste streams which contain a variety of contaminants, often used for drinking water purification.Disadvantages - high operating expense, incomplete oxidation may create chlorinated organic molecules (if Cl2 is used), generation of oxidizing agent typically cannot vary with fluctuating contaminant concentrations.
55CHEMICAL OXIDATION - Results Halogenated aliphatic destruction by H2O2 and UV at 20oC.
56CHEMICAL OXIDATION - Design Considerations Thermodynamics: Free energy available from reactionsOxidant Free Energy (E, volts)OH2OClKinetics: Reaction must proceed to necessary completion within the residence time in the reactor vessel. Combination of UV with ozone or hydrogen peroxide increases reaction kinetics .Design Steps:1) Will oxidation reaction proceed with contaminants present?2) What is the contact time necessary between the oxidant and the contaminants present?
57SUPERCRITICAL FLUID EXTRACTION Description - contaminated liquid or solid is placed in a reactor vessel with the extraction fluid, which is heated and pressurised to the critical point (see chart). In treatment of hazardous wastes, fluids most commonly used are water and CO2, some organic solvents may also be used.Uses - supercritical fluid extraction can be used to treat contaminated soils, sediments, sludges, solids or liquids.Advantages - effective treatment for process wastes or extracted soil or groundwater which is either highly contaminated with organic compounds or with very recalcitrant (hard to treat) organicsDisadvantages - expensive, solids must be reduced in size to 100 um to pass through high pressure pumps.
58SUPERCRITICAL FLUID EXTRACTION Reactor Configuration Schematic diagram of reactor for the extraction of organic compounds from water, CO2 is the extraction fluid.
59SUPERCRITICAL FLUID EXTRACTION Solvent Selection Criteria Cost - water, CO2 are least expensiveRecoverability - solvent must be recoverable for process to be economicalHazard in use - SFE involves high temperatures and pressures which reactor vessels must be built to withstandCritical temperature and pressure - the higher the critical T and P of the solvent, the greater the operating expenseDistribution coefficient - determines the solvent/ contaminant ratio which can be used.
60MEMBRANE PROCESSESElectrodialysis - separation of ionic species from water by direct-current electric field. Useful for removal of charged ions and metals from water.Reverse Osmosis - solvent is forced through a semi-permeable membrane by the application of pressures in excess of the osmotic pressure. Useful for removal of metals and some organics.Ultrafiltration - separates dissolved contaminants on the basis of molecular size. Lower limit for molecular weight is approximately 500.
61BIOLOGICAL PROCESSESDescription - biodegradation uses micro-organisms (bacteria) to remove organic contaminants from vapors, liquids or solids. Most organic contaminants are utilized by bacteria as both a carbon and energy source.Uses - biological processes are effective on both process waste streams and remediation of soil and groundwater. Biodegradation systems for soil and groundwater can by designed either in-situ (in place) or ex-situ (removed from the ground).Advantages - low cost, low site disturbance, effective for many organic contaminants.Disadvantages - long clean-up times, not effective for inorganic contaminants, specialized conditions necessary for chlorinated solvent degradation.
62BIOLOGICAL PROCESSES Necessary Constituents: microorganisms capable of degrading contaminantscontaminants in aqueous (water) phaseavailable electron acceptor presentAerobic Degradation: takes place in the presence of molecular oxygen (O2), the most energetically favorable electron acceptor.Anaerobic Degradation: when O2 is not available, other compounds can act as electron acceptors for biodegradation processes, such as NO3, Fe+3, Mn+4, SO4, and CO2.
63Energy Available from Electron Acceptor Processes DGo(kJ/mol mineralized)ElectronAcceptorTolueneBenzeneO-3913-3778-2175-358-37-35662-NO-32453Fe+3, Mn+4~~-2343SO-2-3404CO-1362
64BIOLOGICAL PROCESSES - Remediation of soil and groundwater In-situ biodegradation:Natural attenuationEngineered systemsEx-situ biodegradation:Pump and treat systems for groundwaterLandfarming systems for soil treatment
66Typical Contaminant / Electron Acceptor Concentrations with Distance Natural Attenuation of ContaminantsTypical Contaminant / Electron AcceptorConcentrations with Distance-2-
67Relative Importance of Electron Acceptor Processes at 25 Air Force Sites AerobicMethanogenesisRespiration39%10%Denitrification14%Iron (III)Reduction8%SulfateReduction29%Source: Wiedemeier et al., 1995
68( ) Stoichiometric Conversion Example: Iron Reduction BTEX + 36Fe H2O Fe+2 + 7CO2 + 7H2OAssume 20 mg/l Fe+2 observed in aquiferCalculate BTEX consumed per unit volume:(20 mg/l Fe+2 produced )1 mmol Fe+256 mg Fe+2()1 mmol BTEX36 mmol Fe+292 mg BTEX= 0.9 mg/l BTEX consumed in aquiferCalculate groundwater flux and total BTEX consumed:Assume: Vgw = 1 ft/day Plume width = 100’ Plume height = 10’Flux = vwh = 1000 ft3/d = 7500 gal/d = 28x103 l/dBTEX consumed = (28x103 l/d) (0.9 mg/l) = 25 g BTEX/day
70In-Situ Biodegradation - Engineered Systems Infiltration gallery, recirculating system
71In-Situ Biodegradation - Engineered Systems Combination air injection/extraction systemwater table
72In-Situ Biodegradation - Engineered Systems Air injection bioventing
73Ex-Situ Biodegradation - Pump and treat Water TableLiquidHydrocarbonContaminantSkimmerPumpVacuumAir removalOil/waterSeparatorVacuum PumpLiquid phaseBioreactor
74Ex-Situ Biodegradation - Biofiltration MoistureAdditionBiofilterBlowerVaporExtractionWellContaminated SoilBiofilter is colonized with bacteria capable of degrading contaminants. Media can be soil, peat, compost, or manufactured packing material.
76Ex-Situ Biodegradation - Landfarming Procedures:Excavated soils are spread onto the ground surface to a depth of less than 0.5 meters.Underlying soils should be low permeability, or a clay liner or impermeable membrane should be used to prevent contaminant migration to groundwater.Landfarmed soils should be tilled every 2-3 months and kept moist.
77WASTE STABILIZATION AND CONTAINMENT Procedure: Excavated soils or process wastes are secured such that contaminant migration will not occur (containment), or are mixed with binding agents that solidify the waste and prevent leaching or release of the contaminants (stabilization).Processes:EncapsulationSorption processesPolymer stabilizationIn-situ vitrification
80COMBUSTION METHODSDescription: waste combustion can take place in hazardous waste incinerators, cement kilns, or industrial boilers. Most significant design parameter is the heat value of the waste. Many concentrated organic wastes will support combustion without supplemental fuel.Applicable wastes: all organic wastes can be mineralized using combustion methods. Metals are oxidized in the combustion process and are either vented in gaseous form or are concentrated in ash. Metals prone to gaseous emission are arsenic, antimony, cadmium, and mercury.Procedure: Wastes are graded for suitability for combustion. Waste analysis also indicates the proper fuel/air mixture for complete combustion.
82CONTAINMENTFrecuently it is necessary to minimize the rate of off site contaminant migration employing containments technologies to minimize risk to public health and environment.Containment technologies may be associated with other technologies to implement a long-term clean-up strategy for the site
83CONTAINMENTActive system components require considerable effort and on-going energy in put to operate (For example pumping wells)Pasive system components work without much attention, except maintenance (such a cover)
87SELECTION OF REMEDIAL ALTERNATIVES 1. Data NeedsA. Site CharacterizationB. Regulatory DispositionC. Risk Assessment2. Establishment of Site ObjectivesA. Clean-up Level NecessaryB. Long-term LiabilityC. Costs3. Development and Analysis of AlternativesA. Development of Possible AlternativesB. Analysis of Alternatives for Effectiveness4. Remedial Option Selection, Implementation, and MonitoringA. Remedial Option SelectionB. ImplementationC. Long term Site Monitoring
88SELECTION OF REMEDIAL ALTERNATIVES Data Needs:Understand extent and magnitude of contamination. A thorough site characterization is necessary. Chemical fate and transport must be understood.Determine risk to potential receptors. This is necessary to correctly focus efforts where they are most needed. Typical exposure pathways include groundwater wells and airborne contaminants.Determine what limits or requirements are placed on the clean up by government regulations. It is important to insure that all participants understand and agree on the goal of the remedial effort.
89SELECTION OF REMEDIAL ALTERNATIVES Establishment of Site Objectives:Establishment or negotiation of acceptable clean-up goals is necessary prior to selection of a remedial process.The extent of long-term liability for the site should be considered.Costs of each remedial option must be considered along with the financial means of the financially responsible party. Options for cost assistance should be considered at this stage (national and international).
90SELECTION OF REMEDIAL ALTERNATIVES Development and Analysis of Alternatives:A list of potential remedial alternatives is compiled for further study based on their feasibility to clean up the site.Criteria for selection of a remedial alternative are effectiveness, reliability, cost, time to implementation, and time to clean up.Before a remedial solution is chosen, a detailed plan of implementation should be formulated to insure that the technique is capable of remediating the site to the goals prescribed.
91SELECTION OF REMEDIAL ALTERNATIVES Remedial Option Implementation and Monitoring:After a remedial option is selected, construction contracts and engineering designs must be completed. Can be done by employee engineers or contractor engineers (must be familiar with technology chosen).Long term site monitoring should continue to insure that the solution is working, and that further contaminant migration does not occur. Monitoring should include all applicable media (groundwater, soil vapor, and air).
94LEY 10/98 DE RESIDUOS CONTAMINATED SITES · Depends of Comunidades Autónomas· List of contaminated places (priority to clean-up)· Need to clean-up the site· The responsible of the contamination· The owner of the site